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Impacts of intensive recreational diving on reef corals at Eilat, northern Red Sea
Biological Conservation 105 (2002) 179–187 www.elsevier.com/locate/biocon
Impacts of intensive recreational diving on reef corals at Eilat, northern Red Sea David Zakaia,b, Nanette E. Chadwick-Furmanb,c,* a
Israel Nature and Parks Authority, Eilat District, PO Box 667, Eilat, Israel b Interuniversity Institute for Marine Science, PO Box 469, Eilat, Israel c Faculty of Life Sciences, Bar-Ilan University, Ramat Gan, Israel
Received 12 October 2000; received in revised form 12 July 2001; accepted 8 August 2001
Abstract Coral reefs at Eilat, northern Red Sea, are among the most heavily used in the world for recreational diving, with >250,000 dives per year on only 12 km of coastline. We assessed patterns of dive frequency, diver behavior, and coral damage on selected reefs at Eilat, in order to determine impacts of diving tourism. Frequencies and types of recreational SCUBA dives varied widely between 12 coral reef sites, with > 30,000 dives per year at the most heavily-used sites. Field observations of diver behavior revealed ca 10 incidents of reef contact per dive, mostly via raising of sediments onto the reef, but also involving direct breakage of corals. The proportion of damaged coral colonies varied significantly with the frequency of SCUBA diving, and did not depend upon site topography. We conclude that current rates of recreational diving on some reefs at Eilat are unsustainable, resulting in damage to the majority of stony coral colonies. This study reveals consequences of diving tourism at extremely high levels of use. Our estimate of diver carrying capacity for reefs at Eilat is similar to levels proposed for other reef sites around the world. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Coral reef; Tourism; SCUBA diving; Red Sea; Carrying capacity
1. Introduction Coral reefs worldwide are under stress due to a variety of anthropogenic activities, including pollution, overfishing, and sedimentation resulting from land-use practices (Richmond, 1993; Wilkinson, 1993, 1996). Tourism has been thought of as a low-impact option for coral reef use, relative to extractive practices such as the harvesting of corals and fish for commercial purposes (Talge, 1993). However, recent evidence has demonstrated that reefs may become degraded as a result of poorly planned or intensive tourist use (Jameson et al., 1999; Tratalos and Austin, 2001). Recreational diving by tourists on coral reefs has increased greatly during the past few decades, due to large numbers of divers being trained, and increased interest in and access to remote coral reef areas (Davis and Tisdell, 1995; Harriott et al., 1997). SCUBA divers may unintentionally damage stony corals and other benthic reef organisms * Corresponding author. Fax: +972-8-637-4329. E-mail address: [email protected] (N.E. Chadwick-Furman).
by breaking their skeletons and abrading their tissues (Hawkins and Roberts, 1992). Coral breakage affects biological processes such as growth and sexual reproduction, which may serve as indicators of coral condition for sustainable reef management (Zakai et al., 2000). Currently, a controversy exists concerning the carrying capacity of different types of reefs for recreational diving, and the concept of possible threshold levels of diving above which use is unsustainable over the long term (Rouphael and Inglis, 1997; Tratalos and Austin, 2001). Diver carrying capacity is usually expressed as a maximum number of dives per site per year, and is a measure of the number of dives a site can sustainably support without becoming degraded (reviewed in Jameson et al., 1999). Reef degradation due to diving activity has been quantified in terms of decreased live stony coral cover (Hawkins et al., 1999) or increased damage to corals (Schleyer and Tomalin, 2000). When diving rate is below carrying capacity for a given reef site, coral damage is minimal, but above carrying capacity, coral damage may increase greatly (Chadwick-Furman, 1997;
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Hawkins and Roberts, 1997). The carrying capacity of coral reefs for SCUBA diving appears to depend on a combination of factors that vary between sites, including: (1) the presence of vulnerable types of organisms, such as branching stony corals (Riegl and Cook, 1995; Rouphael and Inglis, 1997; Schleyer and Tomalin, 2000) and sea whips (Chadwick-Furman, 1997), (2) the level of environmental awareness and training of the divers involved (Rouphael and Inglis, 1997), and (3) the presence of other anthropogenic stressors that degrade the reef, such as particulate pollution (Hawkins and Roberts, 1997). In contrast, some factors that vary between reef sites have been shown to be unrelated to diver carrying capacity, such as reef topography (Rouphael and Inglis, 1997). Further research is needed to define more clearly the roles and relative importance of various factors in determining the carrying capacity of coral reefs for diving tourism (reviewed in Tratalos and Austin, 2001). Some of the most heavily-used coral reefs for recreational diving are located at Eilat, Israel, in the northern Red Sea. Due to their proximity to Europe, extensive tourist facilities, and diverse fauna, coral reefs at Eilat are exposed to > 250,000 dives per year along only 12 km of coast, with most dives occurring along < 4 km of fringing reefs inside the Coral Beach Nature Reserve (Meshi and Ortal, 1995; Chadwick-Furman, 1997; Wilhelmsson et al., 1998). During the past few decades, reefs at Eilat have become degraded as a result of a combination of pollution, intensive diving, tourism, and shoreline modification (Loya, 1990; Riegl and Velmirov, 1991; Fishelson, 1995). Their condition has been rated as critical; if management practices are not changed, these reefs are predicted to collapse within 20 years (Wilkinson, 1993). Diving pressure at Eilat is so intense that the use of artificial reefs has been proposed recently to divert divers away from natural reefs in the area (Wilhelmsson et al., 1998). Despite the economic importance of the local dive industry based on coral reefs, few quantitative data is available concerning the relationship between frequencies of SCUBA dives, diver behavior, and damage rates to reef corals at Eilat. A comparison study of one reef site in Eilat with several in Egypt found the Eilat site to be among the most degraded, with up to half of all colonies broken in some coral species (Riegl and Velmirov, 1991). Examination of a no-use zone at Eilat revealed that fewer colonies of the branching coral Stylophora pistillata were broken than in a nearby area open to public use (Epstein et al., 1999). Rates of recreational use were not quantified in either of these two studies. Here, we assess frequencies of recreational diving at 12 coral reef sites in Eilat, frequencies of diver behavior that damage corals, and proportions of damaged corals in relation to dive use levels. We then recommend
options for coral reef management at Eilat that may reduce diver-related damage to ecologically sustainable levels.
2. Methods 2.1. Frequencies and types of SCUBA dives We defined 12 coral reef dive sites along 12 km of coast line at Eilat, Israel, in the northern end of the Gulf of Aqaba, Red Sea (Fig. 1). Ten of the 12 dive sites (nos. 3–12) were located inside the area of the Coral Beach Nature Reserve (CBNR), most of which is open to recreational diving (Fig. 1). Dive sites were defined as those with: (1) the presence of coral reefs, (2) clear entrance points into the water that were regularly used by divers (except for at the North Beach site which extended from the Israeli–Jordanian border to the northern border of the oil terminal area, see Fig. 1), and (3) a 75-m-long area to the south and north from the point of entrance (150 m total) where divers were active
Fig. 1. Map of 12 coral reef dive sites examined at Eilat, Israel, northern Red Sea: (1) North Beach (defined as the Israeli–Jordanian border to the northern border of the oil terminal area, but not including the Dekel dive site), (2) Dekel, (3) Village, (4) Aqua Sport, (5) Northern Reserve, (6) Central Reserve, (7) Japanese Gardens, (8) Lighthouse, (9) Diver’s Village, (10) Caves, (11) Drori, and (12) Tables. #=seven sites chosen for diver behavior survey, *=four sites chosen for coral damage assessment.
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between 4 and 8 m depth. A data table was distributed to 14 commercial dive centers in Eilat, to be completed using dive center logbooks. The number and type of dives at each site were recorded by the dive centers, from 1 January to 31 March, 1996. Data tables were collected regularly from each dive center. Diving activity was classified into three types: (1) introductory dives = uncertified diver guided by a diving instructor, (2) course dives=students in one-star (open water), twostar (advanced open water), and three-star (dive master) certification courses, and (3) guided dives=certified divers guided by a diving instructor or dive master. Dives of independent certified divers were not included since they were not recorded in dive center logbooks. 2.2. Diver behavior During January to May 1997, the behavior of 193 independent and 58 guided certified divers (n=251 total) was studied during 10 min observations per diver (after Rouphael and Inglis, 1997). About 35 divers were observed at each of seven coral reef sites within the CBNR, at 0–30 m depth (Fig. 1). These seven sites were chosen for diver observation because each contained all types of reef topography. Six types of diver behavior were defined, in terms of contact with or damage to the coral reef: hand contact, fin contact, SCUBA tank contact, hose contact, stony coral breakage, and raising of sediments (modified after Harriott et al., 1997; Rouphael and Inglis, 1997). The number of instances of each type of behavior was recorded, as well as the topography of the site (flat, gradual slope, steep slope or patch reef). The divers were not made aware of the presence of observers, in order to ensure natural behavior. To determine whether reef topography affected the rate of contacts to the reef, we used only the 10-min observations of divers who stayed within one topography type. 2.3. Damage to reef-building corals Within the CBNR, four diving sites were chosen that ranged from low to high diving use and that had well developed coral reefs: (1) a low-use site (Japanese Gardens) where only a limited number of guided dives were allowed (1099 total dives per 3 months), (2) a mediumlow-use site (Lighthouse), which had 896 course dives and 599 guided dives (1495 dives per 3 months), (3) a medium-use site (Central Reserve) where mainly guided dives occurred (2029 guided+13 course dives=2042 dives per 3 months) and, (4) a high-use site (Caves) where no limits were placed on divers, and 1395 guided and 2693 course dives occurred (4088 dives total per 3 months; Fig. 2). Field data was collected during November to December 1996, using 20 randomlyplaced 1-m2 quadrats per site (after Hawkins and
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Roberts, 1992; Rouphael and Inglis, 1997) at a depth of 4–8 m, between 75 m north and south of the site entrance point. Inside each quadrat, stony corals were identified as belonging to 10 genera: four branching types (Acropora, Stylophora, Millepora, Pocillopora), four massive types (Favites, Favia, Platygyra, Porites), one foliaceous type (Turbinaria), and one free-living solitary type (Fungia). All other genera of corals were grouped as ‘‘others’’. Within each quadrat, we recorded the number of stony coral colonies of each genus and estimated their percent cover. Coral colonies that were on the quadrat edge were counted only if at least 50% of the colony was within the quadrat area. We also noted the number of coral colonies within each genus that showed evidence of recent damage that was attributable to SCUBA divers (see below). Coral damage that could not be attributed clearly to SCUBA divers was not recorded; we do not quantify here rates of natural damage to corals at Eilat. However, levels of natural damage in 1996 on these reefs were probably low. Natural disturbances, such as coral disease, attacks by the sea star Acanthaster, and tropical storms, were observed to be rare and, in this region, are known to result in low rates of coral damage (Jameson et al., 1999). Two types of diver damage to stony corals were recorded here: (1) skeletal breakage, defined as fractured hard skeleton, and (2) tissue abrasion, defined as damaged tissue that exposed the underlying intact coral skeleton (after Riegl and Velmirov, 1991; Hawkins and Roberts, 1997; Hawkins et al., 1999). Only recent damage was included, as distinguished by white, exposed skeleton in the areas of skeletal breakage or tissue abrasion, which still exhibited all fine coenosteum and calicular structures, and was not overgrown by algae that obscured these structures (after Riegl and Velmirov, 1991). Evidence of diver contact on damaged corals included paint scrapings, fabric threads (Schleyer and Tomalin, 2000) and crushed coral septa indicating impact by a blunt object such as a diver’s fin (Hawkins and Roberts, 1992). Feeding scars made by corallivorous fish and mollusks were distinctive, and were not included as diver damage (Hawkins and Roberts, 1992; Schleyer and Tomalin, 2000). All cases of diver damage, regardless of severity, were counted as colonies with evidence of damage (after Hawkins and Roberts, 1992; Jameson et al., 1999). Within each quadrat, the number of detached, loose branch fragments of living coral adjacent to branching coral colonies was also recorded. Loose fragments were defined as branches of living coral not attached to the substratum, that occurred within 50 cm of attached, broken coral colonies (after Riegl and Riegl, 1996; Hawkins et al., 1999). Statistical analysis of the data was performed using the SAS program, version seven. Percentage data were
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Fig. 2. Estimated number of SCUBA dives per 3 months at 12 coral reef sites in Eilat, Israel, northern Red Sea. Data were collected during 1 January–31 March 1996. The total number of dives per 3 months (dive courses+introductory dives+guided dives)=37,639.
arcsin transformed before ANOVA analyses. Unless otherwise indicated, data are presented as means one standard deviation.
3. Results 3.1. Frequencies and types of SCUBA dives A total of 37,639 guided dives were recorded in 3 months on coral reefs at Eilat (Fig. 2). Most of these dives (76%) occurred within the CBNR (all sites except North Beach and Dekel, Figs. 1 and 2), and most of them (69%) involved the training of uncertified divers (course+ introductory dives). In addition, more than half of the training dives were made inside the CBNR (52% of total dives). The most frequently used sites were the North Beach, Aqua Sport, and Northern Reserve (Fig. 2). The annual guided dive frequency, as calculated from this 3month sample, is > 150,000 guided dives made on coral reefs at Eilat during 1996. This number underestimates diving activity at Eilat, because it does not include certified divers that made independent dives without guides, and only the 3-month low season was sampled. 3.2. Diver behavior Observation of SCUBA divers revealed high frequencies of behaviors that potentially damage the coral
reef. Divers were observed frequently to contact the reef with their fins and to raise sediment onto corals, and some were observed actually breaking corals (Fig. 3). We estimate that on a typical SCUBA dive of 60 min at 4–8 m depth, each recreational diver broke 1.70 4.90 corals and raised 9.40 11.90 sediment clouds onto the reef (n=251 divers). Observation of divers in areas with different reef topographies revealed contact rates (for all six activities above) of 3.6 4.5 contacts per 10 min on flat areas (n=26 divers), 2.5 2.6 contacts on gradual slopes (n=18 divers), 3.4 4.4 contacts on steep slopes (n=37 divers), and 5.5 4.6 contacts on patch reefs (n=46 divers). The rate of contact did not vary significantly with the topographical structure of the coral reef (Kruskal–Wallis test, P=0.85). 3.3. Damage to reef-building corals The percent cover of branching stony corals did not vary significantly between the four examined sites (ANOVA, F=1.70, P=0.17; Fig. 4). Most of the damage observed on branching corals was in the form of broken skeleton, with very little abraded tissue (Fig. 4a). The lowest percent of damaged branching corals (skeletal breakage and tissue abrasion combined) occurred at the Japanese Gardens site (15.4 15.7%). At the Lighthouse site, 40.0 22.3% of branching corals were damaged, at the Central Reserve site 60.6 27.7%
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were damaged, and at the Caves site a very high percentage (80.8 17.0%) of branching corals were damaged. The damage frequency to branching corals varied significantly between sites (ANOVA, F=33.92, P < 0.001, Tukey–Kramer multiple comparisons test, P < 0.05 for all comparisons). The number of loose coral fragments m 2 varied significantly between genera of branching corals and between reef sites (2-way ANOVA, F=29.90 and 7.12 for site and coral genus respectively, and P < 0.001 for both; Fig. 5). Only 0–6 loose coral fragments m 2 were observed at the low-use Japanese Gardens site (for all four branching coral genera combined), while up to 26 fragments m 2 were found at the high-use Caves site (Fig. 5). Colonies of the branching hydrocoral Millepora had the most broken fragments m 2, while those of the more robust scleractinian coral Pocillopora had the fewest (Fig. 5). In contrast to branching corals, the percent cover of massive corals varied significantly between sites (ANOVA, F=6.26, P < 0.001; Fig. 4b). All of the damage observed on massive coral colonies was in the form of tissue abrasion, with no accompanying skeletal breakage (Fig. 4b). Fewer massive corals than branching corals were damaged at each site, but both coral types showed a similar trend of variation in damage between sites (Fig. 4a and b). The damage rate for massive corals was lowest at the Japanese Gardens (5.0 11.5%), intermediate at the Lighthouse (11.8 18.5%) and Central Reserve (35.8 15.3%), and highest at the Caves (57.2 27.8%). Damage to massive corals varied significantly between sites (ANOVA, F(3,76)=33.84, P < 0.001), except for between the Japanese Gardens and
Fig. 3. Behavior of recreational SCUBA divers on coral reefs at Eilat, Israel, northern Red Sea. Rates of six types of activities that cause potential damage to reefbuilding corals. Each diver was observed for 10 min in the coral reef environment.
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Lighthouse sites (Tukey–Kramer multiple comparisons test, P=0.42). Other growth forms of stony corals (foliaceous, encrusting) showed mostly tissue abrasion but also some skeletal breakage (Fig. 4c). The rate of damage to all stony corals varied from low at the Japanese Gardens (8.0 7.0%), to intermediate at the Lighthouse (22.2 11.4%) and Central Reserve (40.6 15.3%), and high at the Caves site, where 66.0 14.1% of all corals exhibited damage (Fig. 4d). The amount of total stony coral damage varied significantly between all four sites (ANOVA, F(3,76)=81.36, P < 0.001, Tukey multiple comparisons test, P < 0.05 for all comparisons). Coral damage frequency depended on recreational dive frequency (curvilinear regression test, R2=0.91,
Fig. 4. Percent cover of live stony corals, and percent of colonies damaged (skeletal breakage or tissue abrasion) at four sites in Eilat, Israel, northern Red Sea. Sites are ordered from low to high dive use. n=20 1-m2 quadrats were examined per site. A. Branching corals, B. Massive corals, C. Others, D. All corals.
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P < 0.001; Fig. 6). The curve of the regression line indicates that virtually no diver-damage may have occurred at very low rates of SCUBA diving (Fig. 6).
4. Discussion Here we advance knowledge concerning diver impacts on coral reefs, by: (1) documenting exceptionally high frequencies of recreational SCUBA diving on these reefs, (2) revealing consequently high levels of coral damage, and (3) estimating diver carrying capacity for this reef area, for comparison with levels proposed for other reef areas around the world. Levels of recreational diving recorded here for Eilat are among the highest known in the world, with only two areas reported to have higher levels: South Africa (Riegl and Riegl, 1996; Schleyer and Tomalin, 2000) and Egypt (Hawkins and Roberts, 1997; Jameson et al., 1999). A recent study on high-use reefs in the Caribbean found substantially lower rates of diving (Tratalos and Austin, 2001) than those reported here (Fig. 2). If dives made by independent certified divers are included, ca 250,000–300,000 dives are made per year at Eilat (Meshi and Ortal, 1995; Wilhelmsson et al., 1998), the highest known frequency of recreational diving on a small reef area ( < 12 km of shoreline) anywhere in the world. At four of the most popular dive sites in Eilat (Fig. 2), levels were far above the ca 5000–6000 dives per year considered in previous studies to be the carrying capa-
Fig. 5. Variation in the number of loose branch fragments with reef site ranging from low to high dive use, and with type of branching coral. n=20 1-m2 quadrats were examined at each site.
city of coral reefs for SCUBA diving (Harriott et al., 1997; Hawkins et al. 1999). We conclude that these currently high levels of recreational diving on some reefs at Eilat are ecologically unsustainable. Rates of coral-damaging behavior by trained divers at Eilat were similar to those observed for divers in Australia (Harriott et al., 1997; Rouphael and Inglis, 1997) and Florida (Talge, 1993). In contrast, frequencies of such behavior by untrained divers, which constitute most of the divers at Eilat, are probably higher than those that we report here. Our results confirm those of previous studies, which have shown that rates of damage do not depend on reef topography (Rouphael and Inglis, 1997). Most contacts with the reef were by the divers’ fins (Fig. 3), as also observed for divers in Australia (Harriott et al, 1997), but not for divers on high-turbulence reefs in South Africa, who frequently grabbed the reef with their hands (Schleyer and Tomalin, 2000). We estimate that > 400,000 instances of coral damage by divers occur each year on reefs at Eilat, and that more than two million sediment clouds are raised onto these reefs each year (total estimated number of dives per yearestimated number of colonies damaged or sediment raised per diver on a typical dive). We propose that the exceptionally high proportion of diver-damaged corals on some reefs at Eilat is due to a combination of factors: (1) most dives involve the training of new, uncertified divers (Fig. 2), (2) many certified divers appeared to have poor buoyancy skills, as reflected in their rates of reef contact (Fig. 3), (3) sites at Eilat had, in 1996, a high percent cover of stony
Fig. 6. Variation in total damage to stony coral colonies (both skeletal breakage and tissue abrasion) with the frequency of recreational SCUBA dives at four reef sites in Eilat, Israel, northern Red Sea. Each circle represents data obtained from corals within a 1-m2 quadrat, n=20 quadrats examined per site.
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corals, and thus more corals available to break per unit area, relative to some other reef areas examined for diver damage (Hawkins and Roberts, 1997; Rouphael and Inglis, 1997; but see Hawkins et al., 1999), and (4) each dive site encompasses a more concentrated, smaller reef area (150 m) than that defined for some other regions (500 m; Hawkins and Roberts, 1997), possibly because many of the dive sites at Eilat consist of small patch reefs or limited areas along fringing reefs. Thus, the number of divers per unit area within each site at Eilat may be higher than at dive sites in other regions where reefs are more extensive. The proportions of damaged corals at Eilat are extraordinarily high, with up to 100% of all corals broken in some quadrats examined at the most heavilyused site (Fig. 6). The relationship of coral damage rate to diving rate reported here is more than four times higher than that known for other coral reef areas (Hawkins and Roberts, 1997; Hawkins et al., 1999). The percentage of diver-damaged coral colonies at the lowuse Japanese Gardens site (8%; Fig. 6) exceeded the level proposed as indicating reef degradation in Egypt (4%; Jameson et al., 1999), and was similar to the damage level recently reported for one species of branching coral at this low-use site (9.1%; Epstein et al., 1999). Despite the difficulty of accurately assessing the carrying capacity of coral reefs for recreational diving tourism, the concept of carrying capacity remains an important and useful tool for coral reef management (Davis and Tisdell, 1995). Estimates of carrying capacity for diving may aid efforts to limit use to sustainable levels for the long-term management of coral reefs. At Eilat, damage rates to corals were relatively low at the Japanese Gardens site that had limited diver access of ca 4000 dives per year (Fig. 6). However, at the Lighthouse site, with 8000 dives per year, the damage rate was more than twice as high on average (Fig. 6), indicating that above ca 5000 dives per year, the percent of damaged corals may increase greatly. Thus, we propose ca 5000– 6000 guided dives per site per year as the carrying capacity for reefs at Eilat, at current levels of diver education and training. This estimated carrying capacity for SCUBA diving is similar to levels proposed recently for coral reefs in Australia (Harriott et al., 1997), the Caribbean (Hawkins et al. 1999), Egypt (Hawkins and Roberts, 1997), and South Africa (Schleyer and Tomalin, 2000). The carrying capacity of a given reef area for diving tourism may be raised by increasing the environmental awareness of divers, which leads to a decrease in the frequency of damaging activities on the reef (Hawkins and Roberts, 1997). This may take the form of short briefings of divers before they enter the water (Medio et al., 1997), or the exclusion of untrained divers (those in courses or on introductory dives) from vulnerable reef areas (Tratalos and Austin, 2001). A recent resurvey of
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reefs at Eilat showed that lower rates of coral breakage, and improved underwater behavior of divers, followed a period of increased environmental awareness and improved reef management (D. Zakai and N.E. Chadwick-Furman, unpublished data). We found that many branching corals were surrounded by detached, loose branch fragments, especially on reefs with high dive use (Fig. 5), as also observed in Eilat by Riegl and Velmirov (1991). The four sites we examined did not differ significantly in their percent cover of vulnerable branching corals, in contrast to studies conducted on reefs in South Africa (Riegl and Riegl, 1996) and Australia (Rouphael and Inglis, 1997). Sites that do have high densities of branching corals may be especially susceptible to damage from diving activities, and their rates of sustainable use may be lower than for sites consisting mainly of massive corals [Riegl and Riegl, 1996; Rouphael and Inglis, 1997; Schleyer and Tomalin, 2000; but see Hawkins et al. (1999) for disease impacts on massive corals]. All instances of coral skeletal breakage at Eilat occurred on branching and not on massive coral types (Fig. 4), as found in studies at other reef areas (Hawkins and Roberts, 1992; Chadwick-Furman, 1997; Rouphael and Inglis, 1997). The total percent cover of live stony corals that we observed at 4–8 m depth at the Japanese Gardens site was similar to that found 25 years ago: 67% cover in 1996 (Fig. 4d) compared to 69% cover in 1969 (Loya and Slobodkin, 1971). Thus the Japanese Gardens site, which received a limited, low frequency of recreational dives, had retained a high percent cover of live corals, and in 1996 appeared to be in good condition relative to other, more impacted reef areas at Eilat (Fig. 4). All four sites that we examined had similar levels of percent coral cover. However, as mentioned above, percent cover is not the only measure of diver damage to corals. High proportions of broken or abraded corals may also indicate unsustainable levels of recreation on coral reefs. No data on rates of diver damage were collected at Eilat 25 years ago, so direct comparisons are not possible However, since the frequency of SCUBA diving has increased greatly (Hawkins and Roberts, 1994), and the kind of damage we recorded was most likely caused by divers, we consider that that damage will also have increased. Levels of both natural and anthropogenic disturbance to coral reefs vary widely over time and between reef areas. Reefs in areas with turbulent waters or frequent storms may experience naturally-high levels of coral breakage and abrasion (Schleyer and Tomalin, 2000). To date, only only one study of diver damage has quantified the relative importance of diver-caused versus natural damage to corals. Schleyer and Tomalin (2000) showed that, due to turbulent water conditions on coral reefs in South Africa, ca 15–100% of all coral damage was due to natural causes, versus 0–40% attributable to
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recreational divers at each reef site examined. In contrast, the northern Red Sea is an enclosed body of water with low levels of water motion and only rare tropical storms (Hawkins and Roberts, 1992). Pristine reefs here show low frequencies of coral damage from natural causes (ca 0–2% of colonies affected; Jameson et al., 1999). Thus, levels of diver-induced damage reported here (up to 100% of colonies affected; Fig. 6) likely represent a major impact to reef corals in these relatively quiet waters at the northern tip of the Red Sea. We recommend the following changes in reef management to reduce current levels of coral damage caused by divers at Eilat: (1) limit the total number of dives per reef site per year, (2) require that all dives be led by guides, (3) transfer training courses and introductory dives from fragile reefs to more robust sandy areas, (4) divert recreational diver pressure away from overloaded natural coral reefs to artificial reef areas (after Wilhelmsson et al., 1998), and (5) improve the environmental education of divers in certification training courses, by incorporating mandatory sessions on how to behave underwater around coral reefs (after Rouphael and Inglis, 1997). All of these recommendations have been proposed for other reef areas, but in most cases they have not yet been successfully implemented (Harriott et al., 1997; Medio et al., 1997; Hawkins et al., 1999; Schleyer and Tomalin, 2000). The application of a diver management plan incorporating these elements at Eilat may result in substantial reduction of diver-related damage to reef corals at this heavily-used and economically important tourist destination.
Acknowledgements We thank the staff of the Interuniversity Institute for Marine Science in Eilat for providing logistical support for this study, especially Karen Tamaruder for preparation of the graphics. We also thank the Israel Nature and Parks Authority, especially Noam Meshi. Numerous volunteers served as dive buddies during the field work and assisted in collecting information from the diving centers. The manuscript was improved by comments from David Glassom, Karen Tarnaruder, Jeffrey Wielgus, and two anonymous reviewers. Funding was provided in part by a grant from the Society for the Protection of Nature in Israel This study was submitted in partial fulfilment of the requirements for a MSc degree by D.Z. in the Faculty of Life Sciences at Bar Ilan University. References Chadwick-Furman, N.E., 1997. Effects of SCUBA diving on coral reef invertebrates in the U.S. Virgin Islands: implications for the management of diving tourism. In: den Hartog, J.C. (Ed.), Proceedings of the Sixth International Conference on Coelenterate Biology. Nationaal Naturhistorisch Museum. , pp. 91–100.
Davis, D., Tisdell, C., 1995. Recreational SCUBA-diving and carrying capacity in marine protected areas. Ocean & Coastal Management 26, 19–40. Epstein, N., Bak, R.P.M., Rinkevich, B., 1999. Implementation of a small-scale ‘‘no-use zone’’ policy in a reef ecosystem: Eilat’s reeflagoon six years later. Coral Reefs 18, 327–332. Fishelson, L., 1995. Eilat (Gulf of Aqaba) littoral: life on the red line of biodegradation. Israel Journal of Zoology 41, 43–55. Harriott, V., Davis, D., Banks, S., 1997. Recreational diving and its impact in marine protected areas in Eastern Australia. Ambio 26, 173–179. Hawkins, J., Roberts, C.M., 1992. Effects of recreational SCUBA diving on fore-reef slope communities of coral reefs. Biological Conservation 62, 171–178. Hawkins, J., Roberts, C.M., 1994. The growth of coastal tourism in the Red Sea: present and future effects on coral reefs. Ambio 23, 503–508. Hawkins, J., Roberts, C.M., 1997. Estimating the carrying capacity of coral reefs for SCUBA diving. Proceedings of the Eighth International Coral Reef Symposium 2, 1923–1926. Hawkins, J.P., Roberts, C.M., Van’t Hof, T., de Meyer, K., Tratalos, J., Aldam, C., 1999. Effects of recreational SCUBA diving on Caribbean coral and fish communities. Conservation Biology 13, 888–897. Jameson, S.C., Ammar, M.S.A., Saadalla, E., Mostafa, H.M., Riegl, B., 1999. A coral damage index and its application to diving sites in the Egyptian Red Sea. Coral Reefs 18, 333–339. Loya, Y., 1990. Changes in a Red Sea coral community structure: a long-term case history study. In: Woodwekk, G.M. (Ed.), The Earth in Transition: Patterns and Processes of Biotic Impoverishment. Cambridge University Press, Cambridge, pp. 369–383. Loya, Y., Slobodkin, L.B., 1971. The coral reefs of Eilat (Gulf of Eilat, Red Sea). Symposia of the Zoological Society of London 28, 117–139. Medio, D., Ormond, R.F.G., Pearson, M., 1997. Effect of briefings on rates of damage to corals by SCUBA divers. Biological Conservation 79, 91–95. Meshi, N., Ortal, R., 1995. Diving, boating and submarine activities in Eilat Coral Reef Nature Reserve, Gulf of Aqaba. Proceedings of the Second Conference on the Ecosystem of the Gulf of Aqaba in Relation to Enhanced Economic Development and the Peace Process. Interuniversity Institute for Marine Science, Eilat, pp. 30– 31. Richmond, R.H., 1993. Coral reefs: present problems and future concerns resulting from anthropogenic disturbance. American Zoologist 33, 524–536. Riegl, B., Velmirov, B., 1991. How many damaged corals in Red Sea reef systems? A quantitative survey. Hydrobiologia 216/217, 249– 256. Riegl, B., Cook, P.A., 1995. Is damage succeptibility linked to coral community structure? A case study from South Africa. Beitrage zur Palaontologie 20, 65–73. Riegl, B., Riegl, A., 1996. Studies on coral community structure and damage as a basis for zoning marine reserves. Biological Conservation 77, 269–277. Rouphael, A.B., Inglis, G.J., 1997. Impacts of recreational SCUBA diving at sites with different reef topographies. Biological Conservation 82, 329–336. Schleyer, M.H., Tomalin, B.J., 2000. Damage on South African coral reefsand an assesment of their sustainable diving capacity using a fisheries approach. Bulletin of Marine Science 67, 1025–1042. Talge, H., 1993. Impact of recreational divers on scleractinian corals at Loo Key, Florida. Proceedings of the Seventh International Coral Reef Symposium 2, 1077–1082. Tratalos, J.A., Austin, T.J., 2001. Impacts of recreational SCUBA diving on coral communities of the Caribbean island of Grand Cayman. Biological Conservation 102, 67–75.
D. Zakai, N.E. Chadwick-Furman / Biological Conservation 105 (2002) 179–187 Wilhelmsson, D., Ohman, M.C., Stahl, H., Shlesinger, Y., 1998. Artificial reefs and dive tourism in Eilat, Israel. Ambio 27, 764–766. Wilkinson, C.R., 1993. Coral reefs of the world are facing widespread devastation: can we prevent this through sustainable management practices? Proceedings of the Seventh International Coral Reef Symposium 1, 11–21.
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Wilkinson, C.R., 1996. Global change and coral reefs: impacts on reefs, economies and human cultures. Global Change Biology 2, 547–588. Zakai, D., Levy, O., Chadwick-Furman, N.E., 2000. Experimental fragmentation reduces sexual reproductive output by the reefbuilding coral Pocillopora damicornis. Coral Reefs 19, 185–188.
Impacts of intensive recreational diving on reef corals at Eilat, northern Red Sea David Zakaia,b, Nanette E. Chadwick-Furmanb,c,* a
Israel Nature and Parks Authority, Eilat District, PO Box 667, Eilat, Israel b Interuniversity Institute for Marine Science, PO Box 469, Eilat, Israel c Faculty of Life Sciences, Bar-Ilan University, Ramat Gan, Israel
Received 12 October 2000; received in revised form 12 July 2001; accepted 8 August 2001
Abstract Coral reefs at Eilat, northern Red Sea, are among the most heavily used in the world for recreational diving, with >250,000 dives per year on only 12 km of coastline. We assessed patterns of dive frequency, diver behavior, and coral damage on selected reefs at Eilat, in order to determine impacts of diving tourism. Frequencies and types of recreational SCUBA dives varied widely between 12 coral reef sites, with > 30,000 dives per year at the most heavily-used sites. Field observations of diver behavior revealed ca 10 incidents of reef contact per dive, mostly via raising of sediments onto the reef, but also involving direct breakage of corals. The proportion of damaged coral colonies varied significantly with the frequency of SCUBA diving, and did not depend upon site topography. We conclude that current rates of recreational diving on some reefs at Eilat are unsustainable, resulting in damage to the majority of stony coral colonies. This study reveals consequences of diving tourism at extremely high levels of use. Our estimate of diver carrying capacity for reefs at Eilat is similar to levels proposed for other reef sites around the world. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Coral reef; Tourism; SCUBA diving; Red Sea; Carrying capacity
1. Introduction Coral reefs worldwide are under stress due to a variety of anthropogenic activities, including pollution, overfishing, and sedimentation resulting from land-use practices (Richmond, 1993; Wilkinson, 1993, 1996). Tourism has been thought of as a low-impact option for coral reef use, relative to extractive practices such as the harvesting of corals and fish for commercial purposes (Talge, 1993). However, recent evidence has demonstrated that reefs may become degraded as a result of poorly planned or intensive tourist use (Jameson et al., 1999; Tratalos and Austin, 2001). Recreational diving by tourists on coral reefs has increased greatly during the past few decades, due to large numbers of divers being trained, and increased interest in and access to remote coral reef areas (Davis and Tisdell, 1995; Harriott et al., 1997). SCUBA divers may unintentionally damage stony corals and other benthic reef organisms * Corresponding author. Fax: +972-8-637-4329. E-mail address: [email protected] (N.E. Chadwick-Furman).
by breaking their skeletons and abrading their tissues (Hawkins and Roberts, 1992). Coral breakage affects biological processes such as growth and sexual reproduction, which may serve as indicators of coral condition for sustainable reef management (Zakai et al., 2000). Currently, a controversy exists concerning the carrying capacity of different types of reefs for recreational diving, and the concept of possible threshold levels of diving above which use is unsustainable over the long term (Rouphael and Inglis, 1997; Tratalos and Austin, 2001). Diver carrying capacity is usually expressed as a maximum number of dives per site per year, and is a measure of the number of dives a site can sustainably support without becoming degraded (reviewed in Jameson et al., 1999). Reef degradation due to diving activity has been quantified in terms of decreased live stony coral cover (Hawkins et al., 1999) or increased damage to corals (Schleyer and Tomalin, 2000). When diving rate is below carrying capacity for a given reef site, coral damage is minimal, but above carrying capacity, coral damage may increase greatly (Chadwick-Furman, 1997;
0006-3207/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0006-3207(01)00181-1
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Hawkins and Roberts, 1997). The carrying capacity of coral reefs for SCUBA diving appears to depend on a combination of factors that vary between sites, including: (1) the presence of vulnerable types of organisms, such as branching stony corals (Riegl and Cook, 1995; Rouphael and Inglis, 1997; Schleyer and Tomalin, 2000) and sea whips (Chadwick-Furman, 1997), (2) the level of environmental awareness and training of the divers involved (Rouphael and Inglis, 1997), and (3) the presence of other anthropogenic stressors that degrade the reef, such as particulate pollution (Hawkins and Roberts, 1997). In contrast, some factors that vary between reef sites have been shown to be unrelated to diver carrying capacity, such as reef topography (Rouphael and Inglis, 1997). Further research is needed to define more clearly the roles and relative importance of various factors in determining the carrying capacity of coral reefs for diving tourism (reviewed in Tratalos and Austin, 2001). Some of the most heavily-used coral reefs for recreational diving are located at Eilat, Israel, in the northern Red Sea. Due to their proximity to Europe, extensive tourist facilities, and diverse fauna, coral reefs at Eilat are exposed to > 250,000 dives per year along only 12 km of coast, with most dives occurring along < 4 km of fringing reefs inside the Coral Beach Nature Reserve (Meshi and Ortal, 1995; Chadwick-Furman, 1997; Wilhelmsson et al., 1998). During the past few decades, reefs at Eilat have become degraded as a result of a combination of pollution, intensive diving, tourism, and shoreline modification (Loya, 1990; Riegl and Velmirov, 1991; Fishelson, 1995). Their condition has been rated as critical; if management practices are not changed, these reefs are predicted to collapse within 20 years (Wilkinson, 1993). Diving pressure at Eilat is so intense that the use of artificial reefs has been proposed recently to divert divers away from natural reefs in the area (Wilhelmsson et al., 1998). Despite the economic importance of the local dive industry based on coral reefs, few quantitative data is available concerning the relationship between frequencies of SCUBA dives, diver behavior, and damage rates to reef corals at Eilat. A comparison study of one reef site in Eilat with several in Egypt found the Eilat site to be among the most degraded, with up to half of all colonies broken in some coral species (Riegl and Velmirov, 1991). Examination of a no-use zone at Eilat revealed that fewer colonies of the branching coral Stylophora pistillata were broken than in a nearby area open to public use (Epstein et al., 1999). Rates of recreational use were not quantified in either of these two studies. Here, we assess frequencies of recreational diving at 12 coral reef sites in Eilat, frequencies of diver behavior that damage corals, and proportions of damaged corals in relation to dive use levels. We then recommend
options for coral reef management at Eilat that may reduce diver-related damage to ecologically sustainable levels.
2. Methods 2.1. Frequencies and types of SCUBA dives We defined 12 coral reef dive sites along 12 km of coast line at Eilat, Israel, in the northern end of the Gulf of Aqaba, Red Sea (Fig. 1). Ten of the 12 dive sites (nos. 3–12) were located inside the area of the Coral Beach Nature Reserve (CBNR), most of which is open to recreational diving (Fig. 1). Dive sites were defined as those with: (1) the presence of coral reefs, (2) clear entrance points into the water that were regularly used by divers (except for at the North Beach site which extended from the Israeli–Jordanian border to the northern border of the oil terminal area, see Fig. 1), and (3) a 75-m-long area to the south and north from the point of entrance (150 m total) where divers were active
Fig. 1. Map of 12 coral reef dive sites examined at Eilat, Israel, northern Red Sea: (1) North Beach (defined as the Israeli–Jordanian border to the northern border of the oil terminal area, but not including the Dekel dive site), (2) Dekel, (3) Village, (4) Aqua Sport, (5) Northern Reserve, (6) Central Reserve, (7) Japanese Gardens, (8) Lighthouse, (9) Diver’s Village, (10) Caves, (11) Drori, and (12) Tables. #=seven sites chosen for diver behavior survey, *=four sites chosen for coral damage assessment.
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between 4 and 8 m depth. A data table was distributed to 14 commercial dive centers in Eilat, to be completed using dive center logbooks. The number and type of dives at each site were recorded by the dive centers, from 1 January to 31 March, 1996. Data tables were collected regularly from each dive center. Diving activity was classified into three types: (1) introductory dives = uncertified diver guided by a diving instructor, (2) course dives=students in one-star (open water), twostar (advanced open water), and three-star (dive master) certification courses, and (3) guided dives=certified divers guided by a diving instructor or dive master. Dives of independent certified divers were not included since they were not recorded in dive center logbooks. 2.2. Diver behavior During January to May 1997, the behavior of 193 independent and 58 guided certified divers (n=251 total) was studied during 10 min observations per diver (after Rouphael and Inglis, 1997). About 35 divers were observed at each of seven coral reef sites within the CBNR, at 0–30 m depth (Fig. 1). These seven sites were chosen for diver observation because each contained all types of reef topography. Six types of diver behavior were defined, in terms of contact with or damage to the coral reef: hand contact, fin contact, SCUBA tank contact, hose contact, stony coral breakage, and raising of sediments (modified after Harriott et al., 1997; Rouphael and Inglis, 1997). The number of instances of each type of behavior was recorded, as well as the topography of the site (flat, gradual slope, steep slope or patch reef). The divers were not made aware of the presence of observers, in order to ensure natural behavior. To determine whether reef topography affected the rate of contacts to the reef, we used only the 10-min observations of divers who stayed within one topography type. 2.3. Damage to reef-building corals Within the CBNR, four diving sites were chosen that ranged from low to high diving use and that had well developed coral reefs: (1) a low-use site (Japanese Gardens) where only a limited number of guided dives were allowed (1099 total dives per 3 months), (2) a mediumlow-use site (Lighthouse), which had 896 course dives and 599 guided dives (1495 dives per 3 months), (3) a medium-use site (Central Reserve) where mainly guided dives occurred (2029 guided+13 course dives=2042 dives per 3 months) and, (4) a high-use site (Caves) where no limits were placed on divers, and 1395 guided and 2693 course dives occurred (4088 dives total per 3 months; Fig. 2). Field data was collected during November to December 1996, using 20 randomlyplaced 1-m2 quadrats per site (after Hawkins and
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Roberts, 1992; Rouphael and Inglis, 1997) at a depth of 4–8 m, between 75 m north and south of the site entrance point. Inside each quadrat, stony corals were identified as belonging to 10 genera: four branching types (Acropora, Stylophora, Millepora, Pocillopora), four massive types (Favites, Favia, Platygyra, Porites), one foliaceous type (Turbinaria), and one free-living solitary type (Fungia). All other genera of corals were grouped as ‘‘others’’. Within each quadrat, we recorded the number of stony coral colonies of each genus and estimated their percent cover. Coral colonies that were on the quadrat edge were counted only if at least 50% of the colony was within the quadrat area. We also noted the number of coral colonies within each genus that showed evidence of recent damage that was attributable to SCUBA divers (see below). Coral damage that could not be attributed clearly to SCUBA divers was not recorded; we do not quantify here rates of natural damage to corals at Eilat. However, levels of natural damage in 1996 on these reefs were probably low. Natural disturbances, such as coral disease, attacks by the sea star Acanthaster, and tropical storms, were observed to be rare and, in this region, are known to result in low rates of coral damage (Jameson et al., 1999). Two types of diver damage to stony corals were recorded here: (1) skeletal breakage, defined as fractured hard skeleton, and (2) tissue abrasion, defined as damaged tissue that exposed the underlying intact coral skeleton (after Riegl and Velmirov, 1991; Hawkins and Roberts, 1997; Hawkins et al., 1999). Only recent damage was included, as distinguished by white, exposed skeleton in the areas of skeletal breakage or tissue abrasion, which still exhibited all fine coenosteum and calicular structures, and was not overgrown by algae that obscured these structures (after Riegl and Velmirov, 1991). Evidence of diver contact on damaged corals included paint scrapings, fabric threads (Schleyer and Tomalin, 2000) and crushed coral septa indicating impact by a blunt object such as a diver’s fin (Hawkins and Roberts, 1992). Feeding scars made by corallivorous fish and mollusks were distinctive, and were not included as diver damage (Hawkins and Roberts, 1992; Schleyer and Tomalin, 2000). All cases of diver damage, regardless of severity, were counted as colonies with evidence of damage (after Hawkins and Roberts, 1992; Jameson et al., 1999). Within each quadrat, the number of detached, loose branch fragments of living coral adjacent to branching coral colonies was also recorded. Loose fragments were defined as branches of living coral not attached to the substratum, that occurred within 50 cm of attached, broken coral colonies (after Riegl and Riegl, 1996; Hawkins et al., 1999). Statistical analysis of the data was performed using the SAS program, version seven. Percentage data were
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Fig. 2. Estimated number of SCUBA dives per 3 months at 12 coral reef sites in Eilat, Israel, northern Red Sea. Data were collected during 1 January–31 March 1996. The total number of dives per 3 months (dive courses+introductory dives+guided dives)=37,639.
arcsin transformed before ANOVA analyses. Unless otherwise indicated, data are presented as means one standard deviation.
3. Results 3.1. Frequencies and types of SCUBA dives A total of 37,639 guided dives were recorded in 3 months on coral reefs at Eilat (Fig. 2). Most of these dives (76%) occurred within the CBNR (all sites except North Beach and Dekel, Figs. 1 and 2), and most of them (69%) involved the training of uncertified divers (course+ introductory dives). In addition, more than half of the training dives were made inside the CBNR (52% of total dives). The most frequently used sites were the North Beach, Aqua Sport, and Northern Reserve (Fig. 2). The annual guided dive frequency, as calculated from this 3month sample, is > 150,000 guided dives made on coral reefs at Eilat during 1996. This number underestimates diving activity at Eilat, because it does not include certified divers that made independent dives without guides, and only the 3-month low season was sampled. 3.2. Diver behavior Observation of SCUBA divers revealed high frequencies of behaviors that potentially damage the coral
reef. Divers were observed frequently to contact the reef with their fins and to raise sediment onto corals, and some were observed actually breaking corals (Fig. 3). We estimate that on a typical SCUBA dive of 60 min at 4–8 m depth, each recreational diver broke 1.70 4.90 corals and raised 9.40 11.90 sediment clouds onto the reef (n=251 divers). Observation of divers in areas with different reef topographies revealed contact rates (for all six activities above) of 3.6 4.5 contacts per 10 min on flat areas (n=26 divers), 2.5 2.6 contacts on gradual slopes (n=18 divers), 3.4 4.4 contacts on steep slopes (n=37 divers), and 5.5 4.6 contacts on patch reefs (n=46 divers). The rate of contact did not vary significantly with the topographical structure of the coral reef (Kruskal–Wallis test, P=0.85). 3.3. Damage to reef-building corals The percent cover of branching stony corals did not vary significantly between the four examined sites (ANOVA, F=1.70, P=0.17; Fig. 4). Most of the damage observed on branching corals was in the form of broken skeleton, with very little abraded tissue (Fig. 4a). The lowest percent of damaged branching corals (skeletal breakage and tissue abrasion combined) occurred at the Japanese Gardens site (15.4 15.7%). At the Lighthouse site, 40.0 22.3% of branching corals were damaged, at the Central Reserve site 60.6 27.7%
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were damaged, and at the Caves site a very high percentage (80.8 17.0%) of branching corals were damaged. The damage frequency to branching corals varied significantly between sites (ANOVA, F=33.92, P < 0.001, Tukey–Kramer multiple comparisons test, P < 0.05 for all comparisons). The number of loose coral fragments m 2 varied significantly between genera of branching corals and between reef sites (2-way ANOVA, F=29.90 and 7.12 for site and coral genus respectively, and P < 0.001 for both; Fig. 5). Only 0–6 loose coral fragments m 2 were observed at the low-use Japanese Gardens site (for all four branching coral genera combined), while up to 26 fragments m 2 were found at the high-use Caves site (Fig. 5). Colonies of the branching hydrocoral Millepora had the most broken fragments m 2, while those of the more robust scleractinian coral Pocillopora had the fewest (Fig. 5). In contrast to branching corals, the percent cover of massive corals varied significantly between sites (ANOVA, F=6.26, P < 0.001; Fig. 4b). All of the damage observed on massive coral colonies was in the form of tissue abrasion, with no accompanying skeletal breakage (Fig. 4b). Fewer massive corals than branching corals were damaged at each site, but both coral types showed a similar trend of variation in damage between sites (Fig. 4a and b). The damage rate for massive corals was lowest at the Japanese Gardens (5.0 11.5%), intermediate at the Lighthouse (11.8 18.5%) and Central Reserve (35.8 15.3%), and highest at the Caves (57.2 27.8%). Damage to massive corals varied significantly between sites (ANOVA, F(3,76)=33.84, P < 0.001), except for between the Japanese Gardens and
Fig. 3. Behavior of recreational SCUBA divers on coral reefs at Eilat, Israel, northern Red Sea. Rates of six types of activities that cause potential damage to reefbuilding corals. Each diver was observed for 10 min in the coral reef environment.
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Lighthouse sites (Tukey–Kramer multiple comparisons test, P=0.42). Other growth forms of stony corals (foliaceous, encrusting) showed mostly tissue abrasion but also some skeletal breakage (Fig. 4c). The rate of damage to all stony corals varied from low at the Japanese Gardens (8.0 7.0%), to intermediate at the Lighthouse (22.2 11.4%) and Central Reserve (40.6 15.3%), and high at the Caves site, where 66.0 14.1% of all corals exhibited damage (Fig. 4d). The amount of total stony coral damage varied significantly between all four sites (ANOVA, F(3,76)=81.36, P < 0.001, Tukey multiple comparisons test, P < 0.05 for all comparisons). Coral damage frequency depended on recreational dive frequency (curvilinear regression test, R2=0.91,
Fig. 4. Percent cover of live stony corals, and percent of colonies damaged (skeletal breakage or tissue abrasion) at four sites in Eilat, Israel, northern Red Sea. Sites are ordered from low to high dive use. n=20 1-m2 quadrats were examined per site. A. Branching corals, B. Massive corals, C. Others, D. All corals.
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P < 0.001; Fig. 6). The curve of the regression line indicates that virtually no diver-damage may have occurred at very low rates of SCUBA diving (Fig. 6).
4. Discussion Here we advance knowledge concerning diver impacts on coral reefs, by: (1) documenting exceptionally high frequencies of recreational SCUBA diving on these reefs, (2) revealing consequently high levels of coral damage, and (3) estimating diver carrying capacity for this reef area, for comparison with levels proposed for other reef areas around the world. Levels of recreational diving recorded here for Eilat are among the highest known in the world, with only two areas reported to have higher levels: South Africa (Riegl and Riegl, 1996; Schleyer and Tomalin, 2000) and Egypt (Hawkins and Roberts, 1997; Jameson et al., 1999). A recent study on high-use reefs in the Caribbean found substantially lower rates of diving (Tratalos and Austin, 2001) than those reported here (Fig. 2). If dives made by independent certified divers are included, ca 250,000–300,000 dives are made per year at Eilat (Meshi and Ortal, 1995; Wilhelmsson et al., 1998), the highest known frequency of recreational diving on a small reef area ( < 12 km of shoreline) anywhere in the world. At four of the most popular dive sites in Eilat (Fig. 2), levels were far above the ca 5000–6000 dives per year considered in previous studies to be the carrying capa-
Fig. 5. Variation in the number of loose branch fragments with reef site ranging from low to high dive use, and with type of branching coral. n=20 1-m2 quadrats were examined at each site.
city of coral reefs for SCUBA diving (Harriott et al., 1997; Hawkins et al. 1999). We conclude that these currently high levels of recreational diving on some reefs at Eilat are ecologically unsustainable. Rates of coral-damaging behavior by trained divers at Eilat were similar to those observed for divers in Australia (Harriott et al., 1997; Rouphael and Inglis, 1997) and Florida (Talge, 1993). In contrast, frequencies of such behavior by untrained divers, which constitute most of the divers at Eilat, are probably higher than those that we report here. Our results confirm those of previous studies, which have shown that rates of damage do not depend on reef topography (Rouphael and Inglis, 1997). Most contacts with the reef were by the divers’ fins (Fig. 3), as also observed for divers in Australia (Harriott et al, 1997), but not for divers on high-turbulence reefs in South Africa, who frequently grabbed the reef with their hands (Schleyer and Tomalin, 2000). We estimate that > 400,000 instances of coral damage by divers occur each year on reefs at Eilat, and that more than two million sediment clouds are raised onto these reefs each year (total estimated number of dives per yearestimated number of colonies damaged or sediment raised per diver on a typical dive). We propose that the exceptionally high proportion of diver-damaged corals on some reefs at Eilat is due to a combination of factors: (1) most dives involve the training of new, uncertified divers (Fig. 2), (2) many certified divers appeared to have poor buoyancy skills, as reflected in their rates of reef contact (Fig. 3), (3) sites at Eilat had, in 1996, a high percent cover of stony
Fig. 6. Variation in total damage to stony coral colonies (both skeletal breakage and tissue abrasion) with the frequency of recreational SCUBA dives at four reef sites in Eilat, Israel, northern Red Sea. Each circle represents data obtained from corals within a 1-m2 quadrat, n=20 quadrats examined per site.
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corals, and thus more corals available to break per unit area, relative to some other reef areas examined for diver damage (Hawkins and Roberts, 1997; Rouphael and Inglis, 1997; but see Hawkins et al., 1999), and (4) each dive site encompasses a more concentrated, smaller reef area (150 m) than that defined for some other regions (500 m; Hawkins and Roberts, 1997), possibly because many of the dive sites at Eilat consist of small patch reefs or limited areas along fringing reefs. Thus, the number of divers per unit area within each site at Eilat may be higher than at dive sites in other regions where reefs are more extensive. The proportions of damaged corals at Eilat are extraordinarily high, with up to 100% of all corals broken in some quadrats examined at the most heavilyused site (Fig. 6). The relationship of coral damage rate to diving rate reported here is more than four times higher than that known for other coral reef areas (Hawkins and Roberts, 1997; Hawkins et al., 1999). The percentage of diver-damaged coral colonies at the lowuse Japanese Gardens site (8%; Fig. 6) exceeded the level proposed as indicating reef degradation in Egypt (4%; Jameson et al., 1999), and was similar to the damage level recently reported for one species of branching coral at this low-use site (9.1%; Epstein et al., 1999). Despite the difficulty of accurately assessing the carrying capacity of coral reefs for recreational diving tourism, the concept of carrying capacity remains an important and useful tool for coral reef management (Davis and Tisdell, 1995). Estimates of carrying capacity for diving may aid efforts to limit use to sustainable levels for the long-term management of coral reefs. At Eilat, damage rates to corals were relatively low at the Japanese Gardens site that had limited diver access of ca 4000 dives per year (Fig. 6). However, at the Lighthouse site, with 8000 dives per year, the damage rate was more than twice as high on average (Fig. 6), indicating that above ca 5000 dives per year, the percent of damaged corals may increase greatly. Thus, we propose ca 5000– 6000 guided dives per site per year as the carrying capacity for reefs at Eilat, at current levels of diver education and training. This estimated carrying capacity for SCUBA diving is similar to levels proposed recently for coral reefs in Australia (Harriott et al., 1997), the Caribbean (Hawkins et al. 1999), Egypt (Hawkins and Roberts, 1997), and South Africa (Schleyer and Tomalin, 2000). The carrying capacity of a given reef area for diving tourism may be raised by increasing the environmental awareness of divers, which leads to a decrease in the frequency of damaging activities on the reef (Hawkins and Roberts, 1997). This may take the form of short briefings of divers before they enter the water (Medio et al., 1997), or the exclusion of untrained divers (those in courses or on introductory dives) from vulnerable reef areas (Tratalos and Austin, 2001). A recent resurvey of
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reefs at Eilat showed that lower rates of coral breakage, and improved underwater behavior of divers, followed a period of increased environmental awareness and improved reef management (D. Zakai and N.E. Chadwick-Furman, unpublished data). We found that many branching corals were surrounded by detached, loose branch fragments, especially on reefs with high dive use (Fig. 5), as also observed in Eilat by Riegl and Velmirov (1991). The four sites we examined did not differ significantly in their percent cover of vulnerable branching corals, in contrast to studies conducted on reefs in South Africa (Riegl and Riegl, 1996) and Australia (Rouphael and Inglis, 1997). Sites that do have high densities of branching corals may be especially susceptible to damage from diving activities, and their rates of sustainable use may be lower than for sites consisting mainly of massive corals [Riegl and Riegl, 1996; Rouphael and Inglis, 1997; Schleyer and Tomalin, 2000; but see Hawkins et al. (1999) for disease impacts on massive corals]. All instances of coral skeletal breakage at Eilat occurred on branching and not on massive coral types (Fig. 4), as found in studies at other reef areas (Hawkins and Roberts, 1992; Chadwick-Furman, 1997; Rouphael and Inglis, 1997). The total percent cover of live stony corals that we observed at 4–8 m depth at the Japanese Gardens site was similar to that found 25 years ago: 67% cover in 1996 (Fig. 4d) compared to 69% cover in 1969 (Loya and Slobodkin, 1971). Thus the Japanese Gardens site, which received a limited, low frequency of recreational dives, had retained a high percent cover of live corals, and in 1996 appeared to be in good condition relative to other, more impacted reef areas at Eilat (Fig. 4). All four sites that we examined had similar levels of percent coral cover. However, as mentioned above, percent cover is not the only measure of diver damage to corals. High proportions of broken or abraded corals may also indicate unsustainable levels of recreation on coral reefs. No data on rates of diver damage were collected at Eilat 25 years ago, so direct comparisons are not possible However, since the frequency of SCUBA diving has increased greatly (Hawkins and Roberts, 1994), and the kind of damage we recorded was most likely caused by divers, we consider that that damage will also have increased. Levels of both natural and anthropogenic disturbance to coral reefs vary widely over time and between reef areas. Reefs in areas with turbulent waters or frequent storms may experience naturally-high levels of coral breakage and abrasion (Schleyer and Tomalin, 2000). To date, only only one study of diver damage has quantified the relative importance of diver-caused versus natural damage to corals. Schleyer and Tomalin (2000) showed that, due to turbulent water conditions on coral reefs in South Africa, ca 15–100% of all coral damage was due to natural causes, versus 0–40% attributable to
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recreational divers at each reef site examined. In contrast, the northern Red Sea is an enclosed body of water with low levels of water motion and only rare tropical storms (Hawkins and Roberts, 1992). Pristine reefs here show low frequencies of coral damage from natural causes (ca 0–2% of colonies affected; Jameson et al., 1999). Thus, levels of diver-induced damage reported here (up to 100% of colonies affected; Fig. 6) likely represent a major impact to reef corals in these relatively quiet waters at the northern tip of the Red Sea. We recommend the following changes in reef management to reduce current levels of coral damage caused by divers at Eilat: (1) limit the total number of dives per reef site per year, (2) require that all dives be led by guides, (3) transfer training courses and introductory dives from fragile reefs to more robust sandy areas, (4) divert recreational diver pressure away from overloaded natural coral reefs to artificial reef areas (after Wilhelmsson et al., 1998), and (5) improve the environmental education of divers in certification training courses, by incorporating mandatory sessions on how to behave underwater around coral reefs (after Rouphael and Inglis, 1997). All of these recommendations have been proposed for other reef areas, but in most cases they have not yet been successfully implemented (Harriott et al., 1997; Medio et al., 1997; Hawkins et al., 1999; Schleyer and Tomalin, 2000). The application of a diver management plan incorporating these elements at Eilat may result in substantial reduction of diver-related damage to reef corals at this heavily-used and economically important tourist destination.
Acknowledgements We thank the staff of the Interuniversity Institute for Marine Science in Eilat for providing logistical support for this study, especially Karen Tamaruder for preparation of the graphics. We also thank the Israel Nature and Parks Authority, especially Noam Meshi. Numerous volunteers served as dive buddies during the field work and assisted in collecting information from the diving centers. The manuscript was improved by comments from David Glassom, Karen Tarnaruder, Jeffrey Wielgus, and two anonymous reviewers. Funding was provided in part by a grant from the Society for the Protection of Nature in Israel This study was submitted in partial fulfilment of the requirements for a MSc degree by D.Z. in the Faculty of Life Sciences at Bar Ilan University. References Chadwick-Furman, N.E., 1997. Effects of SCUBA diving on coral reef invertebrates in the U.S. Virgin Islands: implications for the management of diving tourism. In: den Hartog, J.C. (Ed.), Proceedings of the Sixth International Conference on Coelenterate Biology. Nationaal Naturhistorisch Museum. , pp. 91–100.
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